Comparing the Netra smartphone refractor to subjective refraction

Background Among technologies targeting mobile eye care, EyeNetra is a smartphone-based subjective refraction system. This study compared the results from this system with those of professional subjective refraction. Participant visual comfort and preference of results were also measured. Methods Thirty-six optometry-naive participants (n = 36 eyes, aged 18-35 years), were randomly subjected to three refraction methods: professional subjective refraction, unassisted Netra (participants alone) and refined Netra (sphere results refined by a practitioner). Using a randomised, double-blind design, refraction results were mounted in a trial frame and distance logMAR visual acuities were measured. Subjective appreciation and visual comfort were assessed by questionnaire. Overall preference was ranked. Results Unassisted Netra yielded a median myopic overcorrection of 0.60 D (interquartile range [IQR] 0.25 to 0.94) compared to professional subjective refraction. Median equivalent sphere with unassisted Netra (-1.40 D, IQR -3.10 to -0.90) was significantly more myopic than refined Netra (-0.70 D, IQR -1.60 to -0.30) and then subjective refraction (-0.80 D, IQR -1.60 to -0.30) (all p-values < 0.01). Median visual acuity with professional subjective refraction (-0.16, IQR -0.22 to -0.09) was superior than unassisted Netra (-0.08, IQR -0.20 to 0.03) (p < 0.01). Subjective refraction was ranked first in preference of trial framed results by 72 per cent of participants; median preference rank favoured professional subjective refraction to both Netra results (all p < 0.01). For all questionnaire items, visual comfort was higher with subjective refraction than with unassisted Netra (all p < 0.04). Conclusion The Netra device - especially when used without professional assistance and compared to subjective refraction - induces significant myopic overcorrection and lower levels of visual acuity, subjective preference and visual comfort.